CRE Test-2-Solution

# CRE Test-2-Solution - 1 A PFR-CSTR combination is used to...

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1. A PFR-CSTR combination is used to carry out a first order reaction. The PFR is placed in series before a CSTR. The feed concentration to the PFR is C A 0 = 4 mol m -3 and the conversion in the PFR is 65 %. The rate constant is 0.08 s -1 and the feed rate of A is 3 mol s -1 . If the CSTR volume is 1 m 3 , what is the concentration of A after the CSTR? Hence, what is the overall conversion for the PFR-CSTR combination? Solution : First draw a diagram: First we calculate concentration and molar flowrate after the PFR C A1 = C A0 (1-X A1 ) = 4(1-0.65) = 1.4 mol m -3 F A1 = F A0 (1-X A1 ) = 3(1-0.65) = 1.05 mol s -1 Next we must apply the CSTR design equation to the stirred tank. But we must note that the feed to the stirred tank is the outlet stream from the plug flow reactor, and therefore the design equation is: ) ( 2 1 2 A A A R r X F V - = Where in these notes, 2 A X denotes local conversion change across the CSTR. X A2 is reserved to represent overall conversion in the PFR-CSTR combination. As with all applications of the design equation, we have to substitute in a rate equation, in this

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CRE Test-2-Solution - 1 A PFR-CSTR combination is used to...

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